Powders are used in a variety of applications, including medical applications. In one example, it has been proposed to deliver certain types of drugs to patients by inhalation of a powder as a delivery mechanism. One particular example uses diketopiperazine microparticles known as TECHNOSPHERE® microparticles. The TECHNOSPHERE microparticles have a platelet surface structure and can be loaded with a drug. One use of these microparticles is the delivery of insulin by inhalation. An inhaler having a replaceable cartridge or capsule containing the drug powder is used for drug delivery.
In the commercialization of drug delivery by inhalation, large numbers of cartridges containing the drug must be produced in an efficient and economical manner. In particular, the cartridges must be filled with precisely controlled quantities of the powder. While TECHNOSPHERE microparticles are highly effective for drug delivery by inhalation, the platelet surface structure causes TECHNOSPHERE powders to be cohesive and somewhat difficult to handle.
One prior art cartridge filling system includes a feed chamber which delivers powder to a dosing wheel. The dosing wheel, in turn, dispenses controlled quantities of powder into cartridges. The prior art system utilizes vibration and a large paddle wheel to facilitate the flow of powder from a hopper through the feed chamber to the dosing wheel. While the prior art system is generally functional, the energy imparted to the Technosphere microparticles causes the powder to compress and performance to be highly variable. The performance of the prior art system depends, at least in part, on the cohesiveness of the powder being handled, which may range from highly cohesive to free flowing.
Accordingly, there is a need for improved powder feeding methods and apparatus.